This invention relates in general to systems for providing lubrication to rotary drill bits in earth boring systems and in particular to lubrication systems which include means for remotely detecting the imminent failure of the lubrication system.
The lubrication of earth boring drilling systems has long represented a problem in the area. The pressures and temperatures encountered by a rotary drill bit during an earth boring operation may fluctuate over a wide range. At a depth of ten thousand feet, the hydrostatic pressure near the bit may be as high as five thousand psi due to the weight of the drilling fluid in the well bore above the bit. Additionally, the friction of operation and the increase in depth will result in elevated temperatures at and near the drill bit. In order to solve these problems, known systems have been designed with pressure compensators to maintain lubricant pressure within the rotary drill bit. Such pressure compensators typically utilize a flexible membrane or diaphragm situated between a lubricant reservoir and the pressures exerted by the drilling fluid within the well bore. In this manner, the pressures of lubricant and drilling fluid may be equalized and proper lubricant flow to the bearing surfaces can be maintained as the lubricant is forced from the reservoir during higher pressure drilling operations.
It is this variable rate of lubricant utilization which presents a second problem in this area. A rotary drill bit cannot be operated for an extended period of time without lubrication without the possibility of damage to or complete failure of the drill bit. In such cases, the drill bit, or portions of it, may break off and the drill string must be removed and the drill bit must be fished out of the well bore at great expense in both time and effort. As a result, it is a common practice to operate a rotary drill bit for some predetermined period of time and then remove the drill bit and recharge the lubricant reservoir or replace the drill bit. This operation is also time consuming and may be inefficient due to the inability of the drilling operators to accurately gauge the amount of lubrication remaining in a drill bit. Thermocouples and other remote reading instrumentation approaches have not proven practical in this area.